Guidance Software Inc. on Monday said it signed a definitive agreement to acquire substantially all of the assets of Tableau LLC, a privately-held developer and manufacturer of computer forensic hardware, for $12.3 million.

The Pasadena company said the acquisition of Tableau, based in Waukesha, Wis. extends its own capabilities in computer forensics software used in law enforcement, and for legal and corporate uses.

The assets include $1.6 million in cash. Guidance expects the transaction to increase previous revenue guidance by $3 million and be 3 cents per share accretive to non-GAAP earnings in 2010.

Guidance Software has created a forensic business unit, headed by Tableau president Robert Botchek, to better market its products in that sector.

“Tableau is, by far, the leader in forensic hardware, and their products complement our industry-leading EnCase Forensic software,” said Chief Executive Victor Limongelli in a statement.

Shares were down 10 cents, or 1.7 percent, to $5.71 in midday trading on the Nasdaq.