In the months leading up to its deal with First Niagara Financial Group, NewAlliance Bancshares Inc. entertained an offer from another suitor, while continuing to woo a potential acquisition target.

Those details were revealed in a filing with the Securities and Exchange Commission this week.

The $20.4 billion-asset First Niagara in Buffalo approached NewAlliance in December and struck a deal in August to acquire the New Haven, Conn., company for $1.5 billion.

Also in December, an unidentified third company approached NewAlliance CEO Peyton Patterson, and met with her again in February, according to the filing.

Yet an "unexpected development" at the unidentified company in April made it unclear whether and over what time frame further discussions could take place, according to the filing. The company withdrew from consideration in May.

NewAlliance also courted a potential target through June, but ultimately decided not to pursue it, the filing said.

The First Niagara deal was announced Aug. 18, though not before addressing what the filing called a "critical issue" for the NewAlliance board: the role of the NewAlliance management in the combined company, and agreements regarding the compensation of Patterson and Gail Brathwaite, the bank's chief operating officer.

First Niagara's acquisition is expected to close in the first quarter of 2011, pending regulatory and shareholder approval

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