The father of a man who plotted in 2009 to set off homemade bombs in Manhattan subway cars tried to thwart investigators by destroying evidence and misleading a grand jury, a relative testified on Tuesday.

The testimony, in Federal District Court in Brooklyn, came during the trial of Mohammed Wali Zazi, who is charged with obstructing justice and conspiring to obstruct justice while federal agents were investigating his son, Najibullah Zazi.

Mohammed Wali Zazi was among five people who planned to dispose of bomb-making materials, including bleach and nail-polish remover, his brother-in-law Naqib Jaji said in court. Najibullah Zazi had stored the materials in Mr. Jaji’s garage in Colorado, at one point claiming they were ingredients for a fertility potion, Mr. Jaji added.

“He told me he was making medicine to have a baby,” Mr. Jaji said. “If I knew he was making a bomb, I would have called the government.”

Mr. Jaji also testified that Mohammed Wali Zazi asked him to tell a grand jury falsely that Amanullah Zazi, his nephew, was actually an adopted son. Mohammed Wali Zazi told the same lie on immigration forms in 1997, according to federal prosecutors in Manhattan, where he has been indicted on visa fraud.

Mr. Jaji acknowledged lying to a grand jury and to federal investigators about Najibullah Zazi. He said he pleaded guilty last year to conspiring to obstruct justice and signed a cooperation agreement with the government. Amanullah Zazi, who testified on Monday that he destroyed evidence at Mohammed Wali Zazi’s direction, had also pleaded guilty — to charges that included lying to a grand jury — and had signed a similar agreement.

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