VANCOUVER -- Police in Vancouver say they're investigating an unprovoked, violent robbery against a school custodian and are asking witnesses to come forward.

The 38-year-old custodian parked his car near Gladstone Secondary School in South Vancouver just before 5:30 p.m. on Tuesday. Police say two men approached him, and demanded he give them his backpack. 

"When the victim refused, one of the suspects struck the victim on the top of his head with a baton," Const. Tania Visintin said in a news release issued days after the incident.

Police say the men grabbed the backpack and left the area in a dark-coloured SUV that was possibly a Chevrolet. The men drove north on Gladstone Street, then east on East 24th Avenue. 

"One suspect was white. The other suspect's ethnicity is unknown. Both men were wearing dark clothing with no logos, dark baseball caps, and facemasks," the Vancouver police news release said. "The victim was treated by paramedics for bleeding to his head."

Anyone who saw the incident or has information is asked to contact police at 604-717-3321. Tips can also be left anonymously with Crime Stoppers.