WARE, Mass. (WHDH) -- Investigators spent 12 hours Sunday searching for clues all across Ware after receiving an anonymous 9-1-1 call warning of suspicious activity.

The first call was at 8:30 a.m. warning of a possible hazardous material incident on West Street in the vicinity of the high school.

It was a tense afternoon for local residents.

“We really didn't know what was going,” said John Yestramski.

“We took it as a serious threat, a serious phone call,” said Chief Thomas Coulombe of the Ware Fire Department.

Christine Henry didn't return home until late Sunday night. Officers warned her of the threat as she was trying to leave.

“The cop said, 'What are you doing? You can't be leaving, there's a threat in the area and you should stay in your home.’ I said, 'My son has a soccer game.' I didn't know what was going on,” said Henry.

For hours, investigators weren't sure what they were looking for. The threat was called in right near the local middle and high schools.

The search came up empty. Public safety officials have given an all-clear and as a result, school opened Monday morning.

Neighbors were thankful nothing was found, but baffled by the threat.

“I guess we just keep going like nothing happened, ya know, like what else can you do? Unless they tell us something, we don’t know,” said Henry.

Investigators said they are looking into who placed the phone call.