A pair of thieves wearing dust masks stole $13,600 worth of computers from two city elementary schools in the last week by posing as painters.

The incidents are the latest computer-equipment thefts from district buildings in the last school year. District officials said Friday they could not say how much had been stolen. But an internal report obtained by The Inquirer put the value of computers stolen in that period at $615,000.

In the latest crimes, the men, believed to be in their 20s, are sought for the thefts of 12 laptops from Kinsey School in West Oak Lane on July 22 and of an iMac desktop computer from the Pennell School in Ogontz on Wednesday.

In each case, the duo showed up shortly after building engineers opened the schools at 7 a.m. and before most summer employees had arrived.

"We have had a spate of computer thefts over the last two years," said James B. Golden Jr., the district's chief safety executive. "This is the most brazen act I've seen when it comes to computer thefts."

He added, "We're working closely with the Philadelphia Police Department and Northwest Detectives to identify them."

Surveillance videos show that the same men were involved in both thefts. But those who have seen the videos say identifying the culprits may be difficult because the dust masks covered their faces from the top of their noses to below their chins.

A Police Department spokeswoman said officers were called to Kinsey at 5:45 p.m. July 22 when staff realized a dozen Apple laptaps worth $12,000 were missing.

Golden said a Pennell staffer who saw the men on the third floor recalled seeing them "walking around" the building the previous week. The staffer called police, but the men were gone by the time officers arrived.

The district has sent e-mails and memos to building engineers and staff throughout the city, alerting them of the thefts and reminding them of the district's security policy, Golden said. The policy requires visitors to show photo IDs and explain the reason for their visit before they are escorted to the main office.

"That's the standard procedure for building security," Golden said.

Contact staff writer Martha Woodall at 215-854-2789 or martha.woodall@phillynews.com.