WASHINGTON--After only two months of negotiations, Mark Ein, a venture capitalist and former principal of the Carlyle Group, has purchased Kastle Systems International, which installs and manages security systems for multi-tenant commercial office buildings. Terms of the deal were not released.

Kastle, based here with satellite offices in New York, LA, Houston, Dallas, Philadelphia, Chicago, and Sydney, Australia, was founded in 1972 by A. Gene Samburg, who will continue as chief executive officer. Currently, 475 employees service 18,000 buildings, representing 1.85 million cardholders who use the Kastle access control system. Kastle does more than $50 million in annual business.

In an interview, Samburg and Ein expressed a mutual admiration, which contributed to a very quick transaction, a process that began in November 2006.

"This business was not for sale," said Samburg, "but when I met Mark, we developed an instant rapport. Here's a guy who's truly interested in the future of the business ... One of the biggest pluses is Mark's commitment to our employees and our clients going forward."

For Ein's part, he said he was attracted to Kastle's business model--which not only includes substantial installation revenue, but also recurring revenue, as the company manages all the systems it installs--in an industry he called "unbounded in its opportunity."

"This is just one of the most compelling opportunities to get involved in a business with a storied past and lead it into the future," Ein said.

All of Samburg's leadership team will remain in place, Ein said. He called himself an active investor, but "I try to help where I can be helpful and stay out of the way when I need to stay out of the way." Ein, in addition to his work at Carlyle, has been an associate with Goldman Sachs, working in real estate, and on his own provided the seed investment for Matrics Technology and an early investment in XM Satellite Radio, among other investments, largely in telecommunications.

He acknowledged that he hasn't before worked in the security space, "but this is somewhat at the intersection of a lot of things I've done in my career," he said. "I'm very optimistic in this going forward."