An “apparent miscalculation” of the weight of fireworks detonated by police is suspected in the explosion that shook a South Los Angeles neighborhood late last month, according to preliminary findings released Monday.

What was meant to be a safe detonation of homemade fireworks ended in an explosion that injured 17 people, including 11 law enforcement officers, on June 30.

LAPD officers had spent the day seizing a large cache of fireworks from a home. They also reported the discovery of 40 homemade “coke can-sized” devices with powder and fuses on them, and 200 smaller similar devices.

Officials said police opted to detonate some fireworks that were “leaking” and deemed to be too unstable to move, KTLA reports. They loaded the explosive material into a total containment vessel with an iron chamber designed to entirely contain the explosion, according to LAPD.

The officers estimated they were putting in 16.5 pounds of explosives into the vessel, which is designed to take a maximum capacity of 25 pounds for a one-time detonation, LAPD Chief Michel Moore said in a news conference Monday.

But investigators later weighed the remains and calculated that just over 42 pounds of net explosive weight was in the vessel, Moore said.

The LAPD supervisor and bomb technicians involved in the detonation have been removed from the field, Moore said.

It's also suspected that there may have been issues with the vessel itself, which had been in service for more than a decade and used more than 40 times.