Delaware State Police said a man who fatally shot a trooper at a Department of Motor Vehicles office believed he was being monitored and harassed by law enforcement, according to an updated account of the case.

State police said Cpl. Matthew Snook was working an overtime assignment at the New Castle DMV reception desk on Dec. 23, when Rahman Rose entered as a customer and approached him from behind. Investigators said Rose then shot Snook with a handgun.

State police said Rose had no prior interaction with the officer he killed. Investigators also said Rose had limited contact with Delaware law enforcement in the year before the shooting, and that there were no criminal allegations or arrests tied to that contact. They said none of the prior contact involved Snook.

Police said Snook, who went by “Ty,” was a 10-year veteran of the state police force. In the account provided by state police, Snook shielded a DMV employee as he was shot at multiple times.

Investigators said Rose first entered the DMV office on the morning of Dec. 23 and left a short time later. State police said he returned again a few hours later and ambushed the trooper during the second visit.

Earlier, investigators said Rose let customers leave but fired multiple rounds at law enforcement as officers approached the building. State police said a New Castle County police officer shot Rose through a window from outside the building, and Rose later died at a hospital.

In the final update, state police said detectives concluded the attack was deliberate and targeted on law enforcement. The homicide unit cited “the totality of the evidence” in making that determination.

The state police update also described Rose’s views about law enforcement. Investigators said Rose told others he believed police were targeting him and posted on social media about being the victim of “gang stalking,” a belief authorities described as one’s claim that government entities are surveilling and harassing the person.

Police said in a statement that Snook’s “courageous act of strength and sacrifice reflected the core values he lived by every day - protecting others with bravery, selflessness and steady integrity.”