Longueuil police arrested a depanneur clerk following an armed robbery in Greenfield Park.

The strange series of events took place on Lawrence St. in Greenfield Park at 9 p.m. on Sunday, when one man robbed a depanneur.

After the suspect fled the 56-year-old depanneur clerk allegedly picked up a knife, ran after the thief, and attempted to stab him.

A passerby intervened and stopped the attack, and was cut in the face for his trouble.

When police arrived they arrested the clerk, and paramedics took the 28-year-old alleged thief to hospital for medical treatment and a psychological evaluation.

Officers questioned the clerk and released him with a promise to appear in court on a later date to face charges of armed assault.

Police are recommending charges of armed robbery against the alleged thief.