Horace Danby was arrested  although he failed to profit from the robbery  at Shootover Grange, because he broke open the safe to give the lady in red the jewels, thinking her to be the wife of the owner who had forgotten the number combination to open the safe. ... Thus he was arrested  soon afterwards.

Horace Danby was caught for the Shotover Grange robbery due to several factors that led to his identification and arrest.

Mistake in Disposal of Stolen Items

One of the reasons that led to Horace Danby's arrest was his mistake in disposing of the stolen items. He sold a stolen pearl necklace to a pawnbroker, who later realized that it was part of the stolen loot from Shotover Grange. The pawnbroker informed the police, who traced the necklace back to Horace Danby.

Fingerprint Evidence

The police also found fingerprints at the scene of the crime, which matched Horace Danby's fingerprints. The police compared the fingerprints found at the crime scene to the ones they had on file from Horace Danby, which led to his identification and arrest.

Eyewitnesses

There were also eyewitnesses who saw Horace Danby near Shotover Grange around the time of the robbery. The police took statements from these witnesses, which helped in identifying Horace Danby as a suspect.

Confession

Lastly, Horace Danby confessed to the crime. He wrote a letter to the owner of Shotover Grange, expressing his remorse and returning the stolen items. The letter was intercepted by the police, who used it as evidence against him.

Conclusion

In conclusion, Horace Danby was caught for the Shotover Grange robbery due to his mistake in disposing of the stolen items, fingerprint evidence, eyewitness testimony, and his confession. These factors all contributed to his identification and arrest by the police.