OAKLAND -- One man was slain and four others wounded in shootings across Oakland between Sunday afternoon and early Monday, police said.

Killed in a shooting Sunday was Michael Johnson, 22, of Oakland. Johnson was playing dice with a group that included a 24-year-old Oakland man who was also shot in the 1700 block of 103rd Avenue about 2:40 p.m., according to police.

Officer Phong Tran said the group was approached by at least two gunmen, who began shooting at them. Police don't believe robbery was the motive in the shooting, and investigators have not ruled out the possibility the shooting was gang-related, Tran said. He has not yet determined who was the intended target. The gunmen fled on foot and were being sought.

At 1 p.m. Sunday, a 20-year-old man said he had been playing basketball at Arroyo Viejo Park in the 7700 block of Krause Avenue in East Oakland when he heard gunfire and saw he had been grazed in the back.

He was taken to a hospital later by relatives and was in stable condition. No motive was released and no arrests were made.

About 1:13 p.m. Sunday, a 20-year-old man was shot in the lower body near the intersection of Goss and Wood streets in West Oakland. He was in critical condition at a hospital. No motive was released in the shooting and no arrests were made.

At 12:52 a.m. Monday, a 21-year-old man told police he had just left Interstate 580 and was driving in the area of 106th Avenue and Foothill Boulevard in East Oakland when someone started shooting at his car. He sustained a graze wound to his head, but police were not sure if it was from shattered glass or a bullet. He was taken to a hospital, where he was in stable condition. The man did not know why anyone would shoot at him; no arrests were made.

The killing was Oakland's 40th homicide of the year. Last year at this time, there were 45 homicides in the city.

Police and Crime Stoppers of Oakland are offering up to $15,000 in reward money in the fatal shooting and up to $5,000 in the other shootings for information leading to the arrest of suspects. Anyone with information may call police at 510-238-3821 or 510-238-3426 or Crime Stoppers at 510-777-8572.