The brother of one of the victims of a deadly blast in Acre that left five people dead said Monday that the incident was a pre-meditated murder, not a tragic accident as was initially suspected.

Police say it will take time to probe the blast, which leveled a building in the Old City of Acre early Monday, killing members of two families and injuring 12.

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.”

Police indicated that the investigation was being hampered by difficulty in gathering evidence.

“Just to reach all the findings, in all the ruins, this will stretch on for days,” said police commander Eli Asayig. “Everything is buried under the ruins, and it is still dangerous to go in there and dig, until we evacuate all the remains that could collapse in the surrounding area. In any event, from the initial investigation, no remains of explosives were found at the site.”

Local residents 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.

“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.

Asayig said police were investigating the possibility that the incident was a criminal act.

“We are also checking the criminal direction, with the story of opposing antennas that were on the building, and also in the direction of negligence or a technical failure with the gas,” he said. “We can’t even get the gas balloons out of the building because of the destruction, nor can we determine if they were balloons used by the building or brought there.”

The death toll was raised to five late Monday morning, after rescue forces reported finding three more bodies in the debris of the three-story structure.

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 three-story building located in the old city of Acre.

One man who suffered from serious head trauma was brought to Nahariya’s Western Galilee Medical Center.

Paramedics also brought to Nahariya two men in their twenties in moderate condition with bruising across their bodies, a lightly injured 10-year-old girl who suffered light bruising and grazes, a lightly injured woman, and a one-and-a-half year old baby girl suffering from shock, according to United Hatzalah.

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.