Tensions high in Austin amid ongoing manhunt for serial bomber

The threat in Austin, Texas, amid the serial bombings is so omnipresent that a father has now decided to pull his baby's stroller behind him for fear of running over a tripwire.

"When we took a walk yesterday instead of me pushing her forward, I kind of pulled her behind me," Austin resident Joe Biggs told ABC News. "Because if I'm going to set it off, I'd rather it hit me than hit my baby."

The precaution comes after four blasts have set the Texas city on edge, as investigators are working to determine if a fifth explosion at a FedEx facility about 65 miles away is connected to the earlier bombings.

Biggs, who says he has a military background, is taking the ongoing situation seriously.

"When I hear a threat like this ... I take it very seriously," Biggs said.

"I take my daughter everywhere I go, you know, I'm a full-time dad so you know, we go to the park every day, And now it's kind of like, I have to worry about tripwires," he said.

"Now I have to have to have the same mentality I had when I was in Iraq and Afghanistan, here in Austin, Texas, which to me just blows my mind," he said.

Police have told residents to remain vigilant in reporting not only suspicious packages, which were used in the first three blasts, but also any suspicious bags or objects that appear to be out of place.

Crystal Offutt, who lives near the site of the fourth blast, which police believe was initiated by a tripwire, said that the changing nature of the bombs has sparked more concern for her.

"Before it was all kind of like on the east side, and I think it just stresses that it doesn't matter who you are, or what neighborhood you're in," Offutt told ABC station KTRK the day after the fourth blast.

"I think if we're all more aware, then hopefully we will catch them. We're definitely going to stress it more with our child too, anything you see out of the ordinary, just instantly report it," she said.

One consistent theme heard among residents is a fear of the unknown.

Shonda Mace, who said she lives on the street next to the fourth blast, said that she is fielding questions from friends.

"Everyone's just mostly concerned if we're OK and what's going on, asking what's happening, giving me updates, and asking if I know a cause, which I don't know a cause," Mace told Fox affiliate KTBC.

"I don't understand why this is happening," she said.