Debevoise & Plimpton and Wachtell Lipton Rosen & Katz have taken lead roles on Altegrity's $1.13bn (£780m) purchase of risk consultancy Kroll, reports The Am Law Daily.

Debevoise advised Altegrity with a team led by M&A partner Kevin Rinker alongside finance partner Paul Brusiloff, intellectual property partner Jeffrey Cunard, employee benefits partner Jonathan Lewis, and tax partner Peter Schuur.

Meanwhile, Wachtell was instructed by Kroll parent company Marsh & McLennan after taking a role for the professional services firm on its acquisition of Kroll six years ago.

M&A partner Daniel Neff, the co-chair of Wachtell's executive committee, took the lead role along with corporate partners Gregory Ostling and James Cole, antitrust partner Ilene Gotts, executive compensation partner Michael Segal, tax partners Jodi Schwartz and Eiko Stange, real estate partner Stephen Gellman and restructuring partners Eric Rosof and Joshua Feltman.

Private security services firm Altegrity is hoping that the acquisition will make it the detective agency of choice for corporate clients and law firms.

Altegrity was sold to private equity firm Providence Equity Partners in May 2007 for $1.5bn (£1bn) and Debevoise has advised the PE firm on several major media and information deals in recent years, including the $686m (£473m) acquisition of Casema Holding from France Telecom in February 2003 and the formation of a $12bn (£8.3bn) buyout fund in February 2007.

Providence and Altegrity reportedly beat several other suitors to acquire Kroll's speciality services, including private equity firms The Carlyle Group, Apax Partners, and General Atlantic.

Debevoise's Rinker says that his firm's own experience using Kroll's services was instrumental in helping Altegrity as the client conducted its own due diligence into Kroll's various business units.

"We actually involved some of my litigation partners so they could give their views of the market for litigation support services and expanse to various vendors," Rinker said. "That was an interesting twist in this transaction and Kroll OnTrack is a big piece of the Kroll business."

"This was a just another classic leveraged buyout that took place despite the destabilising financing markets," Rinker added. "But at least we got it to this stage."

The Am Law Daily is the website of The American Lawyer, Legal Week's US sister title.