Question: John Surratt was suspected in involvement of the assassination of what president who was killed in April 1865?

Context paragraphs:
Mary Surratt: Mary Elizabeth Jenkins Surratt (1820 or May 1823 – July 7, 1865) was an American boarding house owner who was convicted of taking part in the conspiracy to assassinate U.S. President Abraham Lincoln.  Sentenced to death, she was hanged and became the first woman executed by the US federal government.  She maintained her innocence until her death, and the case against her was and is controversial.  Surratt was the mother of John H. Surratt, Jr., who was later tried but was not convicted of involvement in the assassination.

Surratt House Museum: The Surratt House (also known as the Mary Surratt House and the Surratt House Museum) is a historic house and house museum located at 9110 Brandywine Road in Clinton (formerly Surrattsville), Prince George's County, Maryland, United States.  The house is named for John and Mary Surratt, who built it in 1852.  Mary Surratt was hanged in 1865 for being a co-conspirator in the Abraham Lincoln assassination.  It was acquired by the Maryland-National Capital Park and Planning Commission (M-NCPPC) in 1965, restored, and opened to the public as a museum in 1976.

George Gould (businessman): George Gould (6 April 1865 – 26 May 1941) was a New Zealand farmer, businessman, stock breeder, racehorse owner and breeder, and racing administrator.  He was born in Christchurch, New Zealand on 6 April 1865.  His father (1823–1889), a prominent businessman, had the same name.  He was the uncle of George Macdonald.  He was the grandfather of British politician, Bryan Gould.

David Herold: David E. Herold was born in Maryland, the sixth of 11 children of Adam George Herold (June 6, 1803 – October 6, 1864) and Mary Ann Porter (January 8, 1810 – February 16, 1883).  Adam and Mary were married on November 9, 1828 in Washington, DC.  David was their only son to survive to adulthood.  His father Adam was the Chief Clerk of the Naval Storehouse at the Washington Navy Yard for over 20 years.  Herold's family was well-off financially and lived in a large brick house at 636 Eighth Street SE in Washington, D.C., near the Washington Navy Yard.  David attended Gonzaga College High School, Georgetown College, Charlotte Hall Military Academy (at Charlotte Hall, St. Mary's County, Maryland), and the Rittenhouse Academy.  In 1860 Herold received a certificate in pharmacy from Georgetown College.  He then worked as a pharmacist's assistant and as a clerk for a doctor, and was an avid hunter.  He became acquainted with John Surratt while attending classes at Charlotte Hall Military Academy in the late 1850s.  A few years later, in December 1864, Surratt introduced him to John Wilkes Booth.

Henry Stanhope Freeman: Henry Stanhope Freeman (died April 1865) was the first Governor of the Lagos Colony, serving from 22 January 1862 to April 1865.

Abraham Lincoln: Abraham Lincoln ( ; February 12, 1809 – April 15, 1865) was an American politician and lawyer who served as the 16th President of the United States from March 1861 until his assassination in April 1865.  Lincoln led the United States through its Civil War—its bloodiest war and perhaps its greatest moral, constitutional, and political crisis.  In doing so, he preserved the Union, paved the way to the abolition of slavery, strengthened the federal government, and modernized the economy.

John Surratt: John Harrison Surratt, Jr. (April 13, 1844 – April 21, 1916) was accused of plotting with John Wilkes Booth to kidnap US President Abraham Lincoln and suspected of involvement in the Abraham Lincoln assassination.  His mother, Mary Surratt, was convicted of conspiracy and hanged by the US government; she owned the boarding house that the conspirators as a safe house and to plot the scheme.

Bruce by-election, April 1865: The April 1865 Bruce by-election was a New Zealand by-election held in the multi-member electorate of Bruce during the 3rd New Zealand Parliament on 8 April 1865 triggered by the resignation of Member of Parliament Thomas Gillies.

Mary E. Surratt Boarding House: The Mary E. Surratt Boarding House in Washington, D.C. was the site of meetings of conspirators to kidnap and subsequently to assassinate U.S. President Abraham Lincoln.  It was operated as a boarding house by Mary Surratt from September 1864 to April 1865.

Charles W. Dolloff: Corporal Charles W. Dolloff (May 10, 1844 to August 2, 1884) was an American soldier who fought in the American Civil War.  Dolloff received the country's highest award for bravery during combat, the Medal of Honor, for his action during the Third Battle of Petersburg in Virginia on 2 April 1865.  He was honored with the award on 24 April 1865.

Supporting paragraphs: John Surratt Abraham Lincoln
Answer: Abraham Lincoln