Police are reconstructing the suspect’s movements in the days leading up to the fatal shooting of UnitedHealthcare CEO Brian Thompson. Thompson was killed outside a Manhattan hotel on Wednesday, but police say the suspected gunman had previously been in the city for more than a week.

The suspected shooter was traveling on a Greyhound bus that started its route in Atlanta, law enforcement sources told CNN. Sources said authorities don’t know whether the suspect boarded the ship in Atlanta or elsewhere.

The Atlanta Police Department will assist the NYPD in the investigation as necessary, department officials announced Friday.

Police believe the attacker arrived at the New York Port Authority bus terminal on Nov. 24 – 10 days before the shooting – and then checked into the Upper West Side hostel, a police official said.

He then apparently moved through the city, the official said.

The suspected shooter appeared to be wearing a mask for most of his stay at the hostel, law enforcement sources told CNN. According to a source, he was staying in a shared room with two other men. However, police released a picture of the suspect on Thursday showing him without a mask in the hostel.

The suspect left the hostel on November 29 and checked back in on November 30, law enforcement sources told CNN. According to a source, he paid for the facility in cash – using a fake New Jersey driver’s license to check into the hostel, a law enforcement official previously told CNN.