The United States government said Thursday it would investigate the killing in Zimbabwe of a protected lion. An American man, Walter James Palmer, hunted and killed the beloved lion known as Cecil.

U.S. investigators said they had not been able to reach Mr. Palmer, a dentist in Eden Prairie, Minnesota.

Also, President Obama’s administration said it will examine a U.S. public request to send Mr. Palmer to Zimbabwe for legal action. An administration official said the petition had more than 100,000 signatures.