Barr was suspected of killing civilians
In this movie, Barr is shown as an ex-military soldier. Police presume that he has killed five civilians with a sniper rifle as all the clues pointed to him. A couple of years back, Barr killed four men in Kuwait and was not arrested and was let go. The people he killed were a part of the group of rapes who assaulted 28 women.
Barr is innocent
Later in the movie, you would see that Bar is not the shooter, but the actual shooter is Charlie. Barr wanted help; hence he called Jack Reacher as he knew that he was the only person who could help him in this situation and get him out.
Only one victim was intended
They planned to kill online one victim, Oline Archer, and the other four were killed to cover up the crime. They just wanted to show that it seemed like they had other intentions to kill them.
The five victims were not connected
The five murdered people were not linked to each other by any means. They were clean and were just killed to encase the murder of Oline Archer. (See The Matrix (1999) Movie Explained)
Why Oline Archer was killed
Oline Archer was seen as a hindrance because they wanted her husband’s Quarry, which she refused to sell. The killers had an intention to give the charge of Quarry to someone else and then eventually sell it. Thus, Oline Archer did not agree to it, so they killed her.
Why the killers chose Barr
As Barr had a record of killing people in Kuwait, the killers thought that he would be an easy target as people would not find it hard to believe that he killed more people. (See Red Lights Movie (2012) Ending Explained)
Sandy was a trap
Sandy was a snare made by the bad people who were linked with the murderers. They made this trap to catch Jack, but he was smart enough to make out that it is a trap, so he ignored her.
Emerson is involved in the crime
He is the one who made the plan to include and target Barr to save them. Emerson was completely involved in the offence as he made the plan to frame Barr and was sure that he would be an easy target.
Barr’s story made him innocent
When Helen questioned Barr about how he would have done the crime, Barr explained to her how he would have done it, and it was so different from the way Charlie did it. Barr said it was very professional; after listening to his story, Helen understood that he is innocent.
Barr’s loss of memory made him innocent
His transient loss of memory proved his honesty as he stated the way he would have done the crime was completely distinctive. It was not based on any recent memories but just on his knowledge.