 These factors, says Starr, probably contributed to FitzWalter's increasingly violent behaviour, and by 1340 he was launched on a career of crime during which he terrorised the county.The medieval scholar Ian Mortimer, in what the "Washington Post" reviewer Aaron Leitko called a "Fodor's-style" book—"The Time Traveller's Guide to Medieval England"—says of FitzWalter "nor do you want to come up against" him.In 1340, FitzWalter took part in an incursion of John de Segrave's manor in Great Chesterford.