Police arrested a 14-year-old boy on Friday morning, and detectives were given a further 12 hours to question him. He has since been released on bail until June 17.
Yesterday, a second 14-year-old boy was also arrested, and was bailed until June 1.
Det Insp George Binns, from Preston CID, said: “We have made two arrests and an investigation is very much ongoing.
“We are continuing to ask anybody with information about the fire to come forward. Perhaps you were in the area at the time and saw something suspicious, or perhaps you have other information that could help us. Whatever you know, we would ask you to get in touch as soon as possible.”
Emergency demolition work is underway at the old cinema and nightclub on Church Street and closures remain in place around the building and the area is also closed to pedestrians.
Demolition contractor director Pete Marquis said: “We’re getting on alright at the back of The Odeon; we’ve just took the back wall down which was an issue due to the height, the best part of 11ft high.
"It’s a slow start, it’s a tough old building, it’s not giving in, but we’re away now.
“It won’t be done for the weekend, no way. It will be the middle to back end of next week by the time it’s down. But we’re hoping we can return these streets to normal by Monday evening.”
Anybody with information can call 101, quoting log 1347 of May 19.