Two "fully ready" IEDs were recovered from him and he planned to carry out a "lone wolf" strike at a heavy footfall area in the national
capital, the officials said.
Ahmed said Khan left home on Friday for Rath in UP's Hamirpur district and after that his whereabouts were not known.
"On Saturday, we learnt that he has been arrested in Delhi," he said.
Asked about Khan collecting explosive material and testing bombs in a graveyard, Ahmed said, "I have not heard anything about explosive material. If I had any idea that he was collecting explosive material, I would not have allowed Abu Yusuf to stay in my house."
"Only after the police came in the evening and found the material I realised what it is," he said.
Ahmed said he is "deeply saddened" by what has happened.
"Everyone knows that Abu Yusuf is a very good person. He used to speak very politely, and did not get into fights with anyone," he said.
Khan had been on the police radar for over a year now, according to the officials.
He has been booked under the Unlawful Activities (Prevention) Act. He was remanded to eight days in police custody and taken to different places in Uttar Pradesh, including Balrampur, for further investigation, the officials said.