Farmer Tony Martin, who was jailed for shooting dead a teenage burglar, will not face any charges after being investigated on suspicion of possessing an illegal firearm.
The 71-year-old was arrested last month after a police search of his home, apparently following comments he made to a newspaper reporter about the prevalence of unlicensed firearms in the UK.
Norfolk Police confirmed a firearm seized by officers at the time of Mr Martin's arrest was "was deemed not to be a viable weapon due to its condition" and said he will face no further action.
Mr Martin served three years in prison for shooting dead Fred Barras, 16, at his Norfolk home in 1999 in a case that sparked national debate on the defence of private property.
He was initially found guilty of murder but this was reduced to manslaughter on appeal.
Tony Martin belatedly claimed the Tour de France leader's yellow jersey for the first time on Tuesday with victory on stage four to Cambrai.
Multiple world time-trial champion Martin began the day one second behind maillot jaune incumbent Chris Froome (Team Sky), having been denied the race lead by bonus seconds on Sunday.
The main moment of concern came when Froome wobbled in the gutter after losing his team-mate's wheel.
The 30-year-old was second to Thomas coming off the final cobbled sector and wanted to attack, with Alberto Contador (Tinkoff-Saxo) and Nairo Quintana (Movistar) left behind.
But there was no collaboration in the select eight-man bunch, which included defending champion Vincenzo Nibali (Astana), and Martin next made his successful move.
Froome will be content to have conceded the yellow jersey at this early stage and will hope to add to his British record 15th day in the maillot jaune later in the race.
Farmer Tony Martin, who was jailed for shooting dead a burglar in 1999, has said he confronted a burglar on his property yesterday.
Martin said he decided not to try stopping the would-be burglar, who drove off after being confronted, saying: "I couldn't face going through all that again."
A spokesman for Norfolk Police said: "Police were called to reports of an attempted burglary of outbuildings at a property in Wisbech at around 1.20pm yesterday. Inquiries are ongoing."
Martin was convicted of murder following the 1999 incident but later saw this reduced to manslaughter.