Law enforcement officers from three agencies have checked more than 50 leads but so far no one has been arrested in Sunday’s bombing of a rural Lawrence residence, Douglas County Sheriff Rick Trapp said Wednesday.

“Our officers are keeping busy throughout the day and into the night,” Trapp said during a news conference at the Douglas County Judicial & Law Enforcement Center.

Investigators are trying to determine who is responsible for a bomb that exploded about 3:30 a.m. Sunday inside the house at 1808 N. 1100 Road southeast of Lawrence.

The bomb injured Lloyd Haas Sr., 69, and his wife, Karen Haas, 60. Lloyd Haas is in a Kansas City-area hospital. His condition was upgraded Wednesday from critical to fair, a hospital spokesman said.

A total of 10 sheriff’s officers, three agents from the federal Bureau of Alcohol, Tobacco and Firearms and an agent from the Kansas Bureau of Investigation are working the case full time, Trapp said. ATF and KBI also have offered additional help if needed, he said.

Trapp declined to give many details about the investigation or what happened the morning of the blast at the Haas house. Releasing too many details could make it difficult to verify the legitimacy of information that might be passed on to authorities, he said.

Trapp did say one of the Haases called 911 after the blast.

Lloyd Haas has been interviewed at least once and officers want to talk to him again as his health allows, Trapp said.

Some evidence from the explosion has been sent to an ATF lab for examination, but Trapp wouldn’t describe the evidence.

Trapp also wouldn’t comment on an ongoing dispute Lloyd Haas had with a neighbor and whether it might be connected with the bombing.

“We are taking everything into consideration,” he said.

The sheriff also wouldn’t say if authorities know whether the bombing was a random act or if the Haases were perhaps targeted by someone.

Trapp said he understood the concern neighbors of the Haases have about the incident.

“It’s not something we see generally around Douglas County,” he said. “We’re thankful it’s a rare event in Douglas County.”

Trapp also encouraged anyone who has information that might help the investigation to call 843-TIPS (8477). Callers remain anonymous. Calls can also be made to the Sheriff’s Office at 841-0007.

ATF is offering a reward of $5,000 for information leading to the arrest and conviction of anyone responsible for the bombing. Douglas County Crime Stoppers also is offering up to $1,000 reward through its TIPS hotline.