Businessman Sergei Krasovsky was arrested in the Krasnodar region resort of Anapa, RIA Novosti reported.
Eight other people have been arrested for allegedly being involved in Pakhomov's death, including Yevgeny Kharitonov, 40, a former Moscow Region housing utilities official. Kharitonov was arrested Monday as he was boarding a flight at Moscow's Sheremetyevo airport.
Pakhomov's body was discovered last week, stuffed into a cement barrel in the Moscow Region.
Investigators said Tuesday Pakhomov had likely been murdered over unpaid debts.