DURHAM — An investigation into an assault in a city park has turned into a murder case after the death of a man attacked there in July.

Wayne Preston Cross, 52, died Wednesday from injuries he got when four teenagers attacked him in Long Meadow Park on July 24, police said. They described it as a robbery attempt.

The park, in the 900 block of Holloway Street, had been the site of an earlier assault, and police said at the time of Cross’s attack that they had stepped up patrols in the area about four months earlier to combat violent crime there.

At the time of the attack, police said Cross had received critical injuries. Police did not disclose what caused his death.

Police asked that anyone with information about Cross’s killing call Investigator Pate at 919-560-4440, ext. 29332, or CrimeStoppers at 919-683-1200. CrimeStoppers pays cash rewards for information leading to arrests in felony cases and callers never have to identify themselves.

The week before Cross was attacked, Durham Police Chief Jose Lopez and Sheriff Mike Andrews had met with neighborhood residents to ask them to tell authorities if they had any information about the violence in the park.