A deadly blast that leveled a three-story building in the old city of Acre earlier this week is increasingly looking like a criminal act and not an accidental gas leak, police said Wednesday.

The announcement backs claims by relatives of victims and neighbors that Monday’s explosion, which killed five people from two families and injured 12, happened as part of an ongoing dispute.

Officials said they suspect the blast may have been the act of a single person or a small group, Army Radio reported. They believe the suspect or suspects may have opened a gas canister in the building and placed incendiary material next to it, causing the explosion.

Dozens of people have been questioned in the case, but police earlier said investigation efforts would take time and were hampered by difficulty gathering evidence in the rubble of the building.

No arrests have yet been made.

Local residents on Monday reported a longstanding dispute between the building’s landlord and tenants over the placement of cellular antennas on its top floor. Attempts had reportedly been made to sabotage them in the past.

Many Israelis fear antennas cause ill health effects and violent protests have been held in the past to oppose their placement.

“I think it has to do with the cellular antennas and the quarrel over them but I’m not certain,” neighbor Nadia Amara told Channel 2.

The brother of one of the victims claimed Monday that the incident was a pre-meditated murder, not a tragic accident as was initially suspected.

Initial reports indicated the explosion was caused by a gas leak. However, Khaled Bader, whose brother Muhammad, 43, and sister-in-law, Hanan, 39, were the first two bodies discovered at the scene, called the account “incorrect and unfounded.”

“What happened was murder,” he said, according to Ynet. “We know the people that caused this explosion. These people are irresponsible, we will wait for the funerals to end then we will reveal things that haven’t been said yet. A few weeks ago they threatened me and my family, the threats we received were that they were going to explode the building. My brother and his wife were good people, they got married 15 years ago and they loved each other.”

A second pair of bodies were identified several hours after the blast as another married couple: Najah Sarhan, 35, and her 40-year-old husband, Ra’ek. Rescue forces shortly afterward found the body of their eight-year-old son, Hamed, in the rubble.

The blast that caused the collapse occurred around 2 a.m. on Monday morning.

Rescue personnel at the scene of an explosion that killed five and injured 10 others in the northern city of Acre, Monday , February 17, 2014 (photo credit: Avishag Shaar Yashuv/Flash90)

Rescue personnel at the scene of an explosion that killed five and injured 10 others in the northern city of Acre, Monday , February 17, 2014 (photo credit: Avishag Shaar Yashuv/Flash90)

Five families lived in the building.

On Monday, Public Security Minister Yitzhak Aharonovich visited the site and said every possibility would be investigated.

“It’s possible this was a localized incident or a criminal act, but we must be patient,” he said. He said investigating the incident was “a complex issue which combines several government ministries. It’s still not possible to determine that the explosion was caused by a gas leak.”

In January, a gas explosion in Jerusalem killed four people. including two parents and their 3-year-old child, and left 10 others injured. No foul play was suspected in that incident.