Lying to a law enforcement officer, or anyone in a legal context, is a very ill-advised thing to do. Penalties range from being the subject of close investigation to being charged with perjury or obstruction of justice, according to U.S. Legal; the specifics vary between jurisdictions.
During the course of an investigation or when filing a report, it is crucial to be truthful in every detail being questioned. Knowingly lying to an officer who is investigating is considered obstruction of justice, which is either a misdemeanor or felony charge depending on the severity of the crime. According to US Legal, obstruction of justice also encompasses destruction of evidence and inciting others to lie.
Someone charged with a crime and attempting to lie to officers about evidence will possibly have the sentence compounded with whatever the sentence was for the original crime.
Lying to an officer in an official statement, such as a police report, can incur a fine or jail sentence that varies between jurisdictions. For example, in Massachusetts, a falsified report is punishable by a fine of up to $500, a one-year jail sentence or both, according to the General Court of Massachusetts. Being truthful to law enforcement in all situations is advised.