One Shot

In Pittsburgh, Pennsylvania, a man drives a van into a parking garage across the Allegheny River from PNC Park and, after dropping a quarter into the meter, readies a sniper rifle. He takes aim and kills five people on the river's North Shore Trail from long range before fleeing in the van.
The police soon arrive at the scene of the murder, headed by Detective Emerson (David Oyelowo), and discover a shell casing as well as the quarter used to pay for parking. A fingerprint taken from the coin points to James Barr (Joseph Sikora), a former U.S. Army sniper. When the police raid his house, they find the van, equipment for reloading rifle cartridges, the rifle in question, and Barr asleep in his bed.
During an interrogation by Emerson and the District Attorney, Alex Rodin (Richard Jenkins), Barr is offered a choice between life in prison in exchange for a full confession or guaranteed death row, as Rodin has never failed to convict. Thinking Barr is going to confess when he takes the notepad, they are bewildered when he instead writes "Get Jack Reacher". Jack Reacher (Tom Cruise) is a drifter and former U.S. Army Military Police Corps officer. He arrives in Pittsburgh after seeing a news report about Barr and the shooting. Emerson and Rodin deny Reacher's request to view the evidence but agree to let him see the suspect. Barr, as it turns out, was brutally attacked by fellow inmates while in police custody and is now in a coma. Reacher meets Barr's defense attorney, counselor Helen Rodin (Rosamund Pike), the District Attorney's daughter, who's been saddled with the apparently hopeless task of saving Barr from the death penalty.
Helen says she can arrange for Reacher to see the evidence if he will become her lead investigator. Reacher retorts that he is not interested in clearing Barr. He reveals that Barr had gone on a killing spree during his tour in Iraq but was not prosecuted because, unbeknownst to Barr, his victims were under investigation for numerous rapes and the U.S. Army wanted them forgotten. Reacher vowed that if Barr tried anything like this again, he would take him down.
Reacher agrees to investigate if Helen visits the victims' families to learn about the people murdered that day. Reacher goes to the crime scene and finds inconsistencies about this location, thinking that a trained shooter would have done the killings from the cover of the van on the nearby Fort Duquesne Bridge. After Helen reports her findings about the victims to Reacher, he suggests that the owner of a local construction company was the intended victim, while the other victims served as a cover-up.
After an apparently spurious bar fight, Reacher realizes that someone is attempting to strong-arm him into dropping his investigation. Reacher is later framed for the murder of the young woman who was paid to instigate the bar-room brawl, but this only motivates him further. Reacher eventually follows up a lead at a shooting range in the neighboring state of Ohio, owned by former U.S. Marine Corps Gunnery Sergeant Martin Cash (Robert Duvall), who will talk only if Reacher will demonstrate his U.S. Army sniping skills.
The real perpetrators are gang members masquerading as legitimate businessmen. The gang's elderly leader (Werner Herzog) spent much of his life in a Soviet Gulag and is known only as the Zec (prisoner). The gang kidnaps Helen with the aid of Detective Emerson and holds her hostage at a quarry. Reacher outwits the mob guards, killing them with Cash's help, before confronting the Zec about the conspiracy. Zec points out that Reacher has killed most of the witnesses against him and doubts that he would be convicted. In the interest of justice Reacher shoots the Zec in the head on the spot.
Reacher and Cash flee the scene with confidence that Helen will clear Reacher's name. When Barr awakens from his coma, he tells Helen that he has no recent memory but believes that he must be guilty of the shootings. Barr's mental reconstruction of how he would have committed the shootings confirms that Reacher's theory was correct from the beginning. Still unaware of all these developments, Barr is willing to confess and accept his punishment, fearing that Reacher will mete out justice if the law does not.

Question: who  attempting to strong-arm him into dropping reacher investigation
Answer: someone; someone