VISTA, Calif. — The San Diego County Sheriff’s Department is asking for the public’s help in tracking down whoever’s responsible for a series of mysterious explosions in Vista.

The most recent explosion happened late Thursday night.

Resident Debbie Gomory says she heard the explosion around 11 p.m. near her home on Vale Terrace Drive.

“I had just gone to bed. I heard this loud ‘boom’ go off. I kept waiting to see if I could hear another one. Never heard another one,” said Gomory.

The sheriff’s bomb-arson unit responded to multiple calls from residents.

Investigators combed through a lot near a senior center and park.

Its unclear whether any evidence was found and there were no reports of any damage or anyone hurt.

That incident followed a series of three explosions Wednesday morning and afternoon.

Investigators say those involved homemade devices that went off in open spaces and parking lots with no obvious target or motive.

There was no property damage and no one was hurt.

Investigators have not confirmed whether the explosions are connected.

A $5,000 reward is now being offered for information that leads to an arrest. Anyone with a tip is urged to call San Diego County Crime Stoppers at 1-888-580-8477.