It sounds like premise of a film examining the morals of a small Flanders town – and that was the position the residents of Zedelgem found themselves after a botched robbery in which panicked thieves threw a safe from their getaway car, leaving €1m in cash fluttering in the road.

The Zedelgem mayor, Patrick Arnou, described it as "a rainstorm of money" enticed dozens from their cars and homes, including one with a broom, to scoop up the notes.

But now police say the money must be returned and those who took it face up to two years in jail if they fail to return the cash.

A veil of suspicion has fallen over the town: neighbours watch neighbours as police go door to door, questioning residents.

"People talk about nothing else any more," said Arnou. "In the street itself, there is an atmosphere of bitterness."

Some residents who missed the illicit windfall said they understood the actions of those who took the money, but insisted the size of the cash pile should have made them think twice. "If it were a €20 note," said 77-year-old Hector Clarysse, "I'd pick it up, too, and join in. If you pick up so much money, you know it's not normal."

It all started when the robbers broke into a home in a neighbouring town, and made off with the safe. The getaway car was soon identified and a police motorcycle officer gave chase.

When the chase reached Zedelgem the thieves tried to shake off the officer by throwing the safe in his way. The box shot open, sending a cloud of cash – including €500 notes – into the air.

Dozens of people flooded the street, grabbing handfuls of cash. Drivers got out of their cars, snatched money and sped away. The woman with the broom swept the money into her house, Arnou said.

Police quickly returned and removed cash from those who were too slow in stashing it.

Arnou said authorities have secured nearly half of the €1m. The mayor said residents should have known better, saying: "What we have seen is beyond decency."

Some have handed back what they found, including a couple who drove 60 miles from Antwerp to return €16,200, but not all are so honest. After Arnou designated a postbox outside the town hall for anonymous returns there was an attempt to steal it. It now sits encased deep in concrete.

The case has triggered a passionate debate in Zedelgem. At the Cartouche bar, across the street from the postbox, owner Emely Derous has been moderating both sides.

"Jokingly they say, 'I would have done it this way or that way to keep as much as possible,'" she said. "And yes, I might have done the same thing myself."

For the robbers, the ploy worked. Police attention was diverted trying to recover the cash and they have still not been caught.