“Cincinnati, Thursday, April 26. - About 8 o’clock last night, a party of seven or eight men asked admittance into John Robinson’s circus, at Crittenden, Ky., twenty-seven miles from Covington. Upon being refused, they fired revolvers into the interior of the circus, killing James Robinson, and wounding two other performers. Several audience members were also wounded. The cowardly murderers made their escape.” From the April 27, 1866 New York Times
“James Robinson was not killed in the dastardly affair at the circus at Crittenden, Ky., as reported yesterday, but dangerously wounded. John Alexander Robinson and John Robinson, Jr. were also severely injured. The attacking party numbered twenty-five men, formerly guerrillas. No arrests were made.” From the April 28, 1866 New York Times
The John Robinson Circus was quite an operation, and you can find lots more information about it by Googling it. A hint to the purpose of the shooting is probably in the “formerly guerrillas” description, Civil War feelings still being Very Strong in the state.