Question: What massacre was Peter Gusenberg's brother a victim of?

Context paragraphs:
Barimo massacre: Barimo massacre refers to the massacre of 26 Bosniaks in Barimo, Višegrad in August 1992 by the Bosnian Serb Army.  The victims were mostly women and children.  The entire village was burnt down and destroyed, including religious buildings.  The eldest victim was Hanka Halilović, born in 1900, and the youngest was Fadila Bajrić, born in 1980.

Kingsmill massacre: The Kingsmill massacre took place on 5 January 1976 near the village of Kingsmill in south County Armagh, Northern Ireland.  Gunmen stopped a minibus carrying eleven Protestant workmen, lined them up alongside it and shot them.  Only one victim survived, despite having been shot 18 times.  A group calling itself the South Armagh Republican Action Force claimed responsibility.  It said the shooting was retaliation for a string of attacks on Catholic civilians in the area by Loyalists, particularly the killing of six Catholics the night before.  The Kingsmill massacre was the climax of a string of tit-for-tat killings in the area during the mid-1970s, and was one of the deadliest mass shootings of the Troubles.

Joseph Horn Cloud: Joseph Horn Cloud born 1873 and died September 18, 1920.  His father was Horn Cloud and mother Nest, both parents died at the Wounded Knee Massacre along with two brothers William Horn Cloud (1876-1890), Sherman Horn Cloud (1865-1890) and a niece.  Joseph was a survivor of the massacre as well as his brother Daniel and half brother Dewey Beard [p. 89-95].  Dewey's mother was Yellow Leaf who also died during the massacre.  In the early 1900s a writer named Eli S. Ricker began research for a book he was going to call "The Final Conflict between the Red Men and the Palefaces."  He gathered sources and interviews about conditions and battles on the Plains during the last half of the 1800s.  He recorded the interviews in small note pads known to historians as the "Ricker Tablets."  One such interview was with Joseph telling Ricker what he witnessed at the Wounded Knee Massacre, "When the shooting began the women ran to the ravine.  The shooting was in every direction.  Soldiers shot into one another... Many of the Indians in the circle were killed.  Many of them mingled with the soldiers behind them, picking up guns from dead soldiers and taking cartridge belts."

Don Lee (politician): Don Lee (born 28 February 1960 in Blue Island, Illinois) was the state representative of District 28, consisting of the Columbine/Ken Caryl area of Jefferson County, Colorado, United States from 1998 to 2005.  Columbine High School is located within the district he represented.  He is best known for assisting victim parents from the Columbine High School Massacre in approving the "Respect Life" license plate, raising funds for victims of the Columbine High School Massacre as well as attempting to form an investigative committee to explore any "unanswered questions" about the attacks on Columbine and its aftermath.  Lee was reelected to his fourth term to the Colorado State House of Representatives in 2004 whereupon he promptly resigned therefore paving the way for a Republican vacancy committee to name Jim Kerr as his replacement.  He currently is vice president of government affairs for K12, Inc.

Peter Gusenberg: Peter Gusenberg a.k.a. ""Goosey"" (September 22, 1888 – February 14, 1929) and his brother Frank were German-American contract killers and members of Chicago's North Side Gang, the main rival to the Chicago Outfit.  Peter Gusenberg participated in an infamous attack on Al Capone during a vicious gang war.

Westervelt massacre: The Westervelt massacre, also known as the Westerfield massacre, was an indigenous attack on a caravan of Dutch frontier settlers that occurred during the American Revolutionary War around 3:00 am on June 27, 1780 in Kentucky County, Virginia, the present day state of Kentucky.  It remains one of the largest massacres in Kentucky state history.  The settlers were traveling southeast from Low Dutch Station to Harrod's Town.  The settler relocation was in part a reaction to British Captain Henry Bird's invasion of Kentucky.  The area immediately east of Low Dutch Station had been overrun with British allied Indians.  Harrod's Town was fortified and a move south would lead the settlers away from Captain Bird's invading army from the north.  The caravan was ambushed in a surprise attack, during the night, after a day's travel of twelve miles.  The exact location of the massacre is not definitively known.  However, it is likely to have occurred at Floyd's Fork and Broad Run.  The caravan was formed by Jacobus Westervelt and consisted of forty-one settlers from ten different families.  Ten of the seventeen settlers killed were members of the Westervelt family.  The victims included men, women, and children.  The Indians responsible for the massacre were allied to the British and received ₤5 for each victim's scalp cut off and returned to the British authorities.  The Indians were thus awarded ₤85 by the British for massacring the Dutch settlers.  The Westervelt Massacre had a chilling effect on the region.  A number of settlers from Low Dutch Station joined Colonel George Rogers Clark's militia after the massacre.

Massacre of El Amparo: The Massacre of El Amparo was a massacre of 14 fishermen which took place near the village of El Amparo, in Venezuela's western state of Apure, on 29 October 1988.  A joint military-police unit claimed the fishermen (who had no police records and were not known to either Venezuelan or Colombian military intelligence) were a group of guerillas who attacked them with guns and grenades, with an alleged 15–20 minute exchange of gunfire occurring at a range of 20–30m.  No injuries were sustained by the unit, and an informant from the unit told investigators that the arms that were found amongst the bodies of the fishermen had been planted.  An autopsy performed by Colombian officials on a Venezuelan victim found that he had been shot in the back, his skull crushed by heavy blows, and his face disfigured by acid.  A month later further autopsies were performed by Venezuelan officials, with similar findings; the report was suppressed, but witnesses reported the results.

Frank Gusenberg: Frank Gusenberg (October 11, 1893 – February 14, 1929) was a German-American contract killer and a victim of the Saint Valentine's Day massacre in Chicago, Illinois.

Abhiman Singh Rana Magar: Abhiman Singh Rana Magar (Nepali: अभिमान सिंह राना मगर) was an army general and Minister of Nepal until September 15, 1846, and the first victim of the Kot massacre of 1846.  According to a government letter to then-British Resident, Major Lawrence in Kathmandu, 32 Bhardars (Nobles) were killed in the massacre catapulting Jung Bahadur, who later became Rana, to power.

1922 Turin Massacre: The 1922 Turin Massacre refers to the attack by Italian Fascists against members of a local labour movement in Turin, Italy, during a three-day terror campaign fom 18-20 December 1922.  The events began in Turin after Fascists raided and burned down of a trade union headquarters and attacks on two clubs of the Italian Socialist Party.  This was followed by Fascists taking a number of editors of the newspaper of the Communist Party of Italy hostage, taking them to the central park in Turin and threatening to execute them.  Fascists rounded up communists and trade unionists in the city and executed a number of them in gruesome manners with one victim being tied and dragged behind a truck until he died and another victim being bludgeoned to death.  Eleven people were killed and ten were seriously wounded by the Fascists.

Supporting paragraphs: Peter Gusenberg Frank Gusenberg
Answer: the Saint Valentine's Day massacre