Would you believe that the President of the United States, James Monroe, offered a reward? Here's the screen from the American Presidency Project website with the Proclamation:
The transcription of this proclamation is:
"Proclamation 27 - Offering Reward for the Apprehension of the Murderer of William Seaver
July 10, 1821
"By the President of the United States of America
"Whereas information has been received that an atrocious murder, aggravated by the additional crime of robbery, was on the 6th or 7th dau of this present month, committed in the county of Alexandria and District of Columbia on William Seaver, late of this city, and
"Whereas the apprehension and punishment of the murderer or murderers and his or their or accessary or accessaries will be an example due to justice and humanity and every way salutary in its operation:
"I have therefore thought fit to issue this my proclamation, hereby exhorting the citizens of the United States, and particularly those of this District, and requiring all officers, according to their respective stations, to use their utmost endeavors to apprehend and bring the principal or principals, accessary or accessaries, to the said murder to justice.
"And I do moreover offer a reward for $300 for each principal, if there be more than one, and $150 for each accessary before the fact, if there be more than one, who shall be apprehended after the day of the date hereof and brought to justice, to be paid upon his conviction of the crime or crimes aforesaid.
"In testimony whereof I have caused the seal of the United States to be affixed to these presents, and signed the same with my hand.
"Done at the city of Washington, this 10th day of July, A.D. 1821, and of the independence of the United States the forty-sixth.
By the President:
"JOHN QUINCY ADAMS,
Secretary of State."
The Washington area newspapers carried articles about this proclamation for several mnths, often daily.
In addition, the Mayors of Washington D.C., Georgetown and Alexandria offered a reward, as seen in this newspaper announcement from the Washington Gazette newspaper, dated 16 July 1821 (obtained at GenealogyBank):